U.S. patent number 6,510,121 [Application Number 09/821,670] was granted by the patent office on 2003-01-21 for objective lens driving device including a damping member which has an opening on a main surface to allow an optical axis of a lens to pass through, and optical pickup using the object lens driving device.
This patent grant is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Shinichi Ijima, Hideyuki Nakanishi, Kazutoshi Onozawa, Kazuhiko Yamanaka.
United States Patent |
6,510,121 |
Ijima , et al. |
January 21, 2003 |
OBJECTIVE LENS DRIVING DEVICE INCLUDING A DAMPING MEMBER WHICH HAS
AN OPENING ON A MAIN SURFACE TO ALLOW AN OPTICAL AXIS OF A LENS TO
PASS THROUGH, AND OPTICAL PICKUP USING THE OBJECT LENS DRIVING
DEVICE
Abstract
In a lens driving device for an optical recording/reproducing
apparatus, a lens is held by a platelike damping member that is
made of silicone porous material, for example, and both ends of the
damping member are fixed to a base. This construction prevents
undesired oscillations. Also, in order to drive the lens, two
magnets are attached to an outer edge of the lens opposite to each
other with the lens interposed in between them, and driving coils
are attached to the base facing the magnets. The driving coils have
two coils that drive the lens in the tracking and focusing
directions, respectively.
Inventors: |
Ijima; Shinichi (Takatsuki,
JP), Yamanaka; Kazuhiko (Takatsuki, JP),
Onozawa; Kazutoshi (Takatsuki, JP), Nakanishi;
Hideyuki (Otsu, JP) |
Assignee: |
Matsushita Electric Industrial Co.,
Ltd. (Osaka-fu, JP)
|
Family
ID: |
18607729 |
Appl.
No.: |
09/821,670 |
Filed: |
March 29, 2001 |
Foreign Application Priority Data
|
|
|
|
|
Mar 29, 2000 [JP] |
|
|
2000-092384 |
|
Current U.S.
Class: |
720/684; 359/813;
369/112.23; G9B/7.084; G9B/7.085 |
Current CPC
Class: |
G11B
7/0933 (20130101); G11B 7/0935 (20130101) |
Current International
Class: |
G11B
7/09 (20060101); G11B 007/09 () |
Field of
Search: |
;369/112.23,248,247
;359/814 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Psitos; Aristotelis M.
Claims
What is claimed is:
1. A lens driving device, comprising: a lens; a base a damping
member with fixed parts, the damping member includes a viscoelastic
material which holds the lens in a state of being movable in
relation to the base; and a driving means for driving the lens in a
given direction, wherein the base has space for accommodating the
damping member, and wherein the damping member is platelike in
shape and is suspended in the space of the base, the fixed parts of
the damping member are fixed to the base, the damping member has a
main surface with an opening that passes through the damping
member, and the lens is attached to the damping member in a state
that an optical axis of the lens passes through the opening.
2. The lens driving device of claim 1 wherein the fixed parts being
on both ends of the damping member in a longitudinal direction.
3. The lens device of claim 1, wherein the lens is attached to the
damping member in a state that the optical axis of the lens is
substantially perpendicular to the main surface of the damping
member.
4. An optical pickup comprising: a semiconductor laser component; a
lens for condensing a laser beam emitted from the semiconductor
laser component on a recording surface of an optical recording
medium; a base; a damping member that is made of a material which
is viscoelastic and holds the lens in a state of being movable in
relation to the base, wherein the base has space for accommodating
the damping member, and wherein the damping member is platelike and
suspended in the space in a state that fixed parts of the damping
member are fixed to the base, wherein, on a main surface, the
damping member has an opening that passes through the damping
member, and the lens is attached to the damping member in a state
that an optical axis of the lens passes the opening; a lens driving
means for driving the lens in a given direction; and photoreceptors
that receive a returning laser beam from the optical recording
medium.
5. The optical pickup of claim 4, wherein the fixed parts being on
both ends of the damping member in a longitudinal direction.
6. The optical pickup of claim 4, wherein the lens is attached to
the damping member in a state that the optical axis of the lens is
substantially perpendicular to the main surface of the damping
member.
7. An optical pickup comprising: a semiconductor laser component; a
lens for condensing a laser beam emitted from the semiconductor
laser component on a recording surface of an optical recording
medium; photoreceptors that receive a returning laser beam from the
optical recording medium; an enclosure that holds the lens and
contains the semiconductor laser component and photoreceptors
arranged in a state of having a predetermined positional
relationship; a base; a damping member that is made of a material
which is a viscoelastic and holds the enclosure in a state of being
movable in relation to the base; wherein the base has space for
accommodating the damping member, the damping member is platelike
and suspended in the space in a state that fixed parts of the
damping member are fixed to the base, and wherein, on a main
surface, the damping member has an opening that passes through the
damping member, and the lens is attached to the damping member in a
state that an optical axis of the lens passes the opening; and a
driving means for driving the enclosure in a given direction.
8. The optical pickup of claim 7, wherein the fixed parts being on
both ends of the damping member in a longitudinal direction.
9. The optical pickup of claim 7, wherein the lens is attached to
the damping member in a state that the optical axis of the lens is
substantially perpendicular to the main surface of the damping
member.
Description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a lens driving devise used in an
optical recording/reproducing apparatus for a recording medium such
as a compact disc (CD) and a DVD, and an optical pickup equipped
with such a lens driving device.
(2) Prior Art
In recent years, optical recording/reproducing apparatuses for
compact mass recording media, such as CDs and DVDs, have become
widely used for recording pictures, sounds, and other
information.
An optical recording/reproducing apparatus reads information by
irradiating the recording surface of a recording medium such as an
optical disc with a laser beam using a lens and observing the light
reflected from the recording surface. The information is recorded
along a spiral track on the recording surface.
Here, when the recording medium distorts or deforms, or when a
turntable on which the recording medium is mounted tilts or
precesses, the distance between the recording surface and the lens
changes and the laser beam fails to focus on the recording surface.
Also, when the recording medium or the turntable is decentered, the
track is displaced in the direction of the radius of the medium and
departs from an optical path of the laser beam.
In order to prevent read errors caused by these factors, the lens
is moved up and down in the direction of its optical axis
(hereafter called "focusing direction") to focus the laser beam on
the recording surface. Also, the lens is moved in the direction of
the radius of the medium (hereafter called "tracking direction") to
position the optical path of the laser beam on the track.
To move the lens in such ways, the lens is usually mounted on a
movable member, and a driving unit moves the movable member to
adjust the focal point and the optical path of the laser beam.
Also, the recording medium is rotated at high speed (200-500 rpm in
a CD, 1,000 rpm or higher in a DVD) in the optical
recording/reproducing apparatus, so that the lens has to be quickly
moved to the target position. However, natural oscillations of the
lens driving device or the optical pickup itself cause instability
in the control system.
To suppress the oscillations, Japanese Laid-Open Patent Application
No. H7-105551 discloses a lens driving device in which a movable
member including a lens is held like a cantilever by a fixed member
via a linear elastic supporting member, and a viscoelastic damping
member is positioned on the side of the fixed member surrounding
the root of the elastic supporting member. With this construction,
the oscillations of the elastic supporting member are absorbed by
the damping member, and as a result, the oscillations of the lens
are suppressed.
However, the damping member in the lens driving device described
above is not effective enough to suppress the substantial
oscillations of the elastic supporting member, due to the following
reason. In the oscillations which have the length of the supporting
member as a fundamental wavelength, higher order components are
lower in amplitude than lower order components, so that the higher
order components are difficult for the damping member to
absorb.
Also, because of the construction of the lens driving device in
which the movable member including the lens is held like a
cantilever by the fixed part via the elastic supporting member, the
size of the lens driving device tends to be large in the
longitudinal direction of the elastic supporting member.
SUMMARY OF THE INVENTION
The first object of the present invention is to provide a lens
driving device constructed rationally for an optical
recording/reproducing apparatus. The second object of the present
invention is to provide a lens driving device that effectively
suppresses higher order oscillations. The third object of the
present invention is to provide a lens driving device that is
compact enough to be used for a reproducing apparatus for recording
media such as DVDs. These objects are achieved by a lens driving
device that consists of a lens, a base, a damping member that is
made of a material which is viscoelastic and holds the lens in the
state of being movable in relation to the base, and a driving means
for driving the lens in a given direction.
A material which is viscoelastic can suppress oscillations through
its vibration absorbency. When a lens is held by a supporting
member made of such a material, oscillations of the lens are
suppressed regardless of the direction of the oscillations, and the
size of the lens driving device become smaller.
In addition, the second object of the present invention is to
provide an optical pickup equipped with the lens driving device
descried above. The object can be achieved by an optical pickup
that consists of a semiconductor laser component, a lens for
condensing a laser beam emitted from the semiconductor laser
component on a recording surface of an optical recording medium,
photoreceptors that receive a returning laser beam from the optical
recording medium, an enclosure that holds the lens and contains the
semiconductor laser component and photoreceptors arranged in a
state of having a predetermined positional relationship, a base, a
damping member that is made of a material which is viscoelastic in
any direction and holds the enclosure in the state of being movable
in relation to the base, and a driving means for driving the
enclosure in a given direction.
BRIEF DESCRIPTION OF THE DRAWINGS
These and the other objects, advantages and features of the
invention will become apparent from the following description
thereof taken in conjunction with the accompanying drawings which
illustrate specific embodiments of the invention.
In the drawings:
FIG. 1 is a perspective side view showing a construction of a lens
driving device in the first embodiment of the present
invention;
FIG. 2 shows an assembly of the lens driving device in the first
embodiment;
FIG. 3 is a perspective side view showing a construction of an
optical pickup equipped with the lens driving device of the first
embodiment;
FIG. 4 is a vertical sectional view showing a construction of the
main part of the optical pickup equipped with the lens driving
device;
FIG. 5 is a perspective side view showing a construction of an
optical pickup in the second embodiment of the present
invention;
FIG. 6 is a vertical sectional view showing the construction of the
optical pickup in the second embodiment; and
FIG. 7 is a perspective side view showing a construction of a
modification to the lens driving device of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following describes preferred embodiments of a lens driving
device and an optical pickup of the present invention, with
reference to drawings.
First Embodiment
FIG. 1 is a perspective side view showing an external construction
of a lens driving device 1 in the first embodiment of the present
invention.
As shown in drawing, the lens driving device 1 holds a lens 2 on a
framelike-shaped base 15 via a damping member 20. The lens driving
device 1 moves the lens 2 in the tracking and focusing directions
using two driving units 29 and 30. Here, the driving unit 29 is
made up of a magnet 5 and a driving coil 7, and the driving unit 30
is made up of a magnet 27 and a driving coil 25.
FIG. 2 shows an assembly of the lens driving device 1.
The lens 2 is formed by molding resin. An outer edge 3 of the lens
2 has a pair of notches 4 and 28 opposite to each other. The
substantially rectangular prism magnet 5 is attached in the notch
4, and the substantially rectangular prism magnet 27 is attached in
the notch 28. The magnets 5 and 27 are held with their magnetic
poles pointing in given directions.
The damping member 20 is platelike and made of silicone porous
material (silicone is a generic name for semiorganic polymers in
which each molecule is a chain composed of alternate silicon and
oxygen atoms with an organic group, such as a methyl group,
attached to the silicon atom), and its main surface is shaped like
a letter H. An opening 19, whose caliber is similar to the aperture
of the lens 2, is provided at the center of the main surface. The
lens 2 is positioned so that its optical axis intersects the main
surface of the damping member 20 at approximately right angles (90
degrees) and passes through the opening 19. The outer edge 3 of the
lens 2 is fixed to the damping member 20 with an adhesive or the
like. Also, slots 10 and 21 are arranged in the longitudinal
direction of the damping member 20 with the opening 19 interposed
in between them. The magnet 5 is inserted into the slot 10, and the
magnet 27 is inserted into the slot 21.
Substantially T-shaped protrusions 9, 11, 22, and 23 formed at both
ends of the damping member 20 to play a role like a tenon are fit
into insertion holes 12, 14, 17, and 18 formed on the base 15 to
play a role like a mortise, respectively. In this way, the damping
member 20 is secured to the base 15. Also, step member 13 is formed
between the insertion holes 12 and 14 in an inner edge of the base
15, and a step member 16 is formed between the insertion holes 17
and 18 in an inner edge of the base 15. A driving coil 7 is
positioned on the step member 13 so as to face the magnet 5, and a
driving coil 25 is positioned on the step member 16 so as to face
the magnet 27.
The driving coil 7 is roughly made up of a focusing coil 8 and a
tracking coil 6. The focusing coil 8 and the tracking coil 6 are
wound around one and the same rectangular prism core in the
directions that intersect each other at approximately right angles
(90 degrees). In the same way, the driving coil 25 is roughly made
up of a focusing coil 24 and a tracking coil 26 wound in the
directions that intersect each other at approximately right angles
(90 degrees). When the focusing coil 8 and 24 are excited, magnetic
forces are generated between the focusing coil 8 and the magnet 5
and between the focusing coil 24 and the magnet 27. By these
magnetic forces, the lens 2 is moved in the focusing direction.
Also, when the tracking coils 6 and 26 are excited, magnetic forces
are generated between the tracking coil 6 and the magnet 5 and
between the tracking coil 26 and the magnet 27. As a result of
which, the lens 2 is moved in the tracking direction.
The damping member 20 is made of a gel material. Specifically, the
gel material is a silicone porous material that is formed by
filling a mixture of liquid silicone and a bridging agent in a
metal-mold and then heating it. Elastic capsules of
50-.mu.m-diameter filled with air are mixed into the mixture
beforehand and give porosity to the damping member 20.
The base 15 is formed by molding alloy of aluminum.
FIG. 3 is a perspective side view showing an example optical pickup
equipped with the lens driving device 1. An optical pickup 31 shown
in the drawing uses a swinging arm method. The lens driving device
1 is attached to one end of a swinging arm 32 on the side of an
optical disc 35. A counterbalancing member 34 is attached to the
other end of the swinging arm 32. The swinging arm 32 is balanced
on a pivot 33. The swinging arm 32 is rotated on the pivot 33 in a
plane parallel to the optical disc 35 by a rotation driving
mechanism (not illustrated) so as to trace the track of the optical
disc 35.
FIG. 4 is a vertical sectional view of the optical pickup 31 taken
along a line A--A in FIG. 3. The drawing shows constructions of the
lens driving device 1 and optical members set underneath the lens
driving device 1. For the sake of simplicity, only the section is
shown in the drawing, while the background is not shown. As shown
in the drawing, at the end of the swinging arm 32, a concave is
formed for containing optical components such as a semiconductor
laser device 36, a collimating lens 37, and a raising mirror 38.
The base 15 of the lens driving device 1 is fixed to the swinging
arm 32 with an adhesive or similar to cover the concave.
The semiconductor laser device 36 is a well-known device which is
integrated of a semiconductor laser component as a light-emitting
component, a plurality of photoreceptors as signal detectors, and a
hologram optical component as an optical branch component that
divides incident light.
The optical components such as the semiconductor laser device 36,
the collimating lens 37, and the raising mirror 38 are arranged in
the following fashion. A laser beam emitted from the semiconductor
laser device 36 is collimated by the collimating lens 37, and its
optical path is changed by the raising mirror 38 so that the laser
beam enters the lens 2 with its chief ray almost coincident with
the optical axis of the lens 2.
After passing through the lens 2, the laser beam is condensed on a
recording surface 39 of the optical disc 35, and reflected from the
recording surface 39. The reflected beam regresses the optical path
and returns to the semiconductor laser device 36. The reflected
beam is divided by optical branch components (not illustrated) in
the semiconductor laser device 36 and received by the
photoreceptors. The photoreceptors generate a focusing error
signal, a tracking error signal, and a data signal according to the
amount of the light and output to an control device (not
illustrated).
As described above, the recording surface 39 is displaced due to a
precession, tilt, or the like of the optical disc 35. Accordingly,
in order to read information recorded on the recording surface 39
properly, the focal point of the laser beam has to be followed the
displacement. The control device moves the lens 2 in the focusing
direction by exciting focusing coils 8 and 24 of the driving units
29 and 30 to have the focal point of the laser beam follow the
displacement in the direction of the optical axis according to a
focusing error signal generated by the semiconductor laser device
36.
In the same way, the optical path of the laser beam is followed to
the displacement in the tracking direction by moving the lens 2 in
the tracking direction according to a tracking error signal.
The lens 2 can be moved smoothly by the damping member 20 that
holds the lens 2 because the damping member 20 can deform in any
direction. Also, undesired oscillations of the lens 2 are
suppressed by an oscillation suppressing effect brought by good
absorbency of the material of the damping member 20, silicone
porous material. Therefore, the accuracy of optical reading of the
optical pickup 31 is extremely improved.
In addition, the linear elastic supporting member for holding the
lens and the damping member for suppressing the oscillations of the
elastic supporting member itself are needed in the lens driving
devise disclosed in Japanese Laid-Open Patent Application No.
H7-105551 (shown as a prior art), while the number of members is
reduced in the lens driving devise of this embodiment because the
lens 2 is held directly by the damping member 20. As a result, the
size of the lens driving devise 1 becomes smaller.
Here, silicone porous material is not only viscoelastic in any
direction but weather-resistant and durable, so that life of this
lens driving device become longer than that of the lens driving
device with a damping member made of any other material.
Also, the viscoelasticity of silicone porous material is easily
changed by additives, so that the viscoelasticity of the damping
member 20 can be changed depending on characteristics of the lens
driving device 1 such as weight of the lens 2, the magnet 5, or
27.
In addition, silicone porous material gets other properties by
adding additives. For example, by adding a thermal conductive
filler, the damping member 20 gets thermal conductivity. When a
member of the optical pickup 31, for example the lens 2, is heated
by the laser beam, the damping member 20 transmits the heat of the
lens 2 to other members, so that the lens driving device, as a
whole, performs heatsink and cooling efficiently.
Here, the base 15 is a die-casting made of aluminum alloy, but it
can be made of magnesium alloy or resin.
Second Embodiment
FIG. 5 is a perspective side view of an optical pickup 40 in the
second embodiment of the present invention. A lens 47 is made of
resin, and an outer edge 46 of the lens 47 is attached to steps 53
and 56 in a round-shaped opening, refer to FIG. 6, on the top face
of a enclosure 42. The enclosure 42 is held via a damping member 43
made of silicone porous material by a framelike-shaped base 41.
A magnet 45 and 48 are attached to indentations at the both ends of
the length of the enclosure 42. Driving coils 44 and 49 are fixed
to the base 41 so as to face the magnets 45 and 48, respectively. A
driving unit 50 includes the magnet 45 and the driving coil 44, and
a driving unit 51 includes the magnet 48 and the driving coil 49.
Like the driving coil 7 and 25 in FIG. 1, the driving coils 44 and
49 are roughly made up of focusing coils and tracking coils
respectively wound around one and the same core in the directions
that intersect each other at approximately right angles (90
degrees).
FIG. 6 is a vertical sectional view of the optical pickup 40 taken
along the line B--B shown in FIG. 5. As shown in the FIG. 6, an
integrated light-emitting/receiving component 52 and a raising
mirror 55 are contained in the enclosure 42. The integrated
light-emitting/receiving component 52 is made by packing a
light-emitting component and a plurality of photoreceptors. A
semiconductor laser component is used as the light-emitting
component. The raising mirror 55 has a reflecting hologram surface
54.
A laser beam emitted from the semiconductor laser component on the
integrated light-emitting/receiving component 52 is reflected from
the reflecting hologram surface 54 of the raising mirror 55 and
condensed on a recording surface 58 of an optical disc 57 by the
lens 47. The laser beam reflected from the recording surface 58
regresses on the optical path described above and is divided at the
reflecting hologram surface 54 to enter the photoreceptors on the
integrated light-emitting/receiving component 52.
According to outputs from each photoreceptor, a focusing error
signal, a tracking error signal, and a data signal are generated.
The explanation about how to generate these signals is omitted here
because it is well-known.
When a focal point of the laser beam is displaced from the
recording surface 58 in the focusing direction, the photoreceptors
generate a focusing error signal. According to the focusing error
signal, a current is passed through the focusing coils of the
driving units 50 and 51, and the magnet 45 and 48 are moved in the
focusing direction. As a result, the enclosure 42 containing the
lens 47 is moved in the focusing direction, so that the focal point
of the laser beam is adjusted. When a focal point of the laser beam
is displaced from the recording surface 58 in the tracking
direction, the focal point of the laser beam is adjusted in the
same way.
This embodiment is different from the first embodiment in a point
that optical members, namely the enclosure 42 itself containing the
integrated light-emitting/receiving component 52 and the lens 47,
are moved, so that the chief ray of the laser beam can be placed to
coincide with the optical axis of the lens 47. As a result, optical
characteristics are stably effective because the tracking error
signal is not deteriorated in amplitude or offset even when the
lens 47 is moved in the tracking direction.
Modifications
Although the present invention has been described according to the
embodiments, it is to be noted that the present invention is not
limited to the embodiments described above. The embodiments can be
modified as followings.
(1) Electromagnetic actuators are classified into two types: MC
Type (Moving Coil Type: a movable member has driving coils) and MM
Type (Moving Magnet Type: amovable member has magnets).
Although the first and second embodiment described above are
constructed using only MM Type actuators in which movable members
have magnets, MC Type actuators also can be used. An advantage of
MC Type actuators is that they are easily controlled because
magnets are displaced on a proportional basis to a current passing
through driving coils. On the other hand, MM Type actuators do not
need wiring on the movable member. It is preferred that suitable
type actuators are chosen depending on designs and/or purposes.
(2) Also, it is preferred that a recording surface of an optical
disc intersects the optical axis of a lens at approximately right
angles (90 degrees) in order to read the information on the optical
disc properly. Some conventional lens driving devices generate a
tilting error signal when detecting decentering of a recording
surface. The following modification shows a lens driving device
that changes tilt of the lens according to a tilting error
signal(hereafter called "tilting driving").
The lens driving device in this modification has four driving units
60, 61, 62, and 63 as shown in FIG. 7 in which the driving units 60
and 63 are opposite to the driving units 61 and 62 in the
longitudinal direction of the lens driving device with the lens
interposed in between them.
In this construction, when a different amount of currents is passed
through the focusing coils of the driving units 60 and 61 from the
focusing coils of the driving units 62 and 63, in which two pairs
are opposite to each other with the lens interposed in between
them, torque is produced in the direction of rotating the lens on
an axis that is parallel to the tracking direction, so that the
lens driving device performs the tilt driving in the same
direction. Also, in the same way, when a different amount of
currents is passed through the focusing coils of the driving units
60, 63 from the focusing coils of the driving units 61 and 62, the
lens performs the tilting driving on an axis that is parallel to
the main surface of the damping member and intersects the tracking
direction at approximately right angles (90 degrees). Accordingly,
in this modification, the tilting driving can be performed on two
axises that intersect each other at approximately right angles (90
degrees), so that the tilting driving can be performed in any
direction. Therefore, the focal point of the laser beam can be
followed to the track on the recording surface regardless of the
direction of the tilt of the recording surface. This is effective
to anticipate precession of a turntable of an optical disc.
Here, generally, when two pairs of driving units are arranged in
the direction that intersects the driving direction at
approximately right angles (90 degrees), and their driving
directions are parallel to the optical axis of the lens, the
tilting driving can be performed in any direction by adjusting
driving forces of the driving units. Also, as described above, when
they are arranged in the state of having lines passing across the
optical axis of the lens between them, the tilting driving can be
performed more efficiently.
(3) In the first and second embodiment, a light-emitting component
and photoreceptors are combined, but they can be used in separate
forms. In the case, the optical path of the returning light from
the recording medium is led to the photoreceptors using a half
mirror or a beam splitter.
Here, a component packed of a light-emitting/receiving component
and another optical component also can be used effectively in this
present invention. The first embodiment has an afocal construction
in which the optical members include a collimating lens to follow
the displacement of the lens, while the construction of the second
embodiment is not afocal. However, in both embodiments, this
present invention can be used effectively regardless of choosing
either construction of them.
(4) In the embodiment described above, the base is moved by the
swinging arm method, but a linear motor method or a traverse
driving method using a coarse motor can be used instead.
Also, in the first embodiment, when the lens is made by molding
resin, the magnet attached to the outer edge of the lens can be
molded in the lens as a combination. Also, in the construction
using MC Type actuators, the driving coils can be molded in the
lens as a combination. In the second embodiment, when the base is
made of resin, the magnets or the driving coils can be molded in
the base.
As described above, when the magnet or the driving coils as the
driving member is molded in the lens or the base as the movable
member, the cost of the device reduces, and the characteristics of
the lens driving device are shown stably with accuracy of
positioning of the driving members.
(5) In the embodiment described above, the damping member 20 is
made of silicone porous material, but other gel materials that are
substantially made of silicone can be used instead. The molecular
construction of silicone is changed by additives, so that it can be
adjusted in vibration isolation or in shock absorbing. There are
organic additives and inorganic additives; for vibration isolation,
inorganic additives are used. In the embodiment described above,
the silicone is porous, but adding certain additives, other types
of silicone can be used effectively in the present invention.
An example product of the gel materials is a .alpha.GEL(GELTECH
Co.Ltd.). .alpha.GEL is substantially made of silicone, and the
penetration grade of it (Japanese Industrial Standards
K2530-1976-50 g weight) is 50-200. In the range of 50-200,
.alpha.GEL shows good properties of vibration isolation,
shock-absorbing, and soundproofing. .alpha.GEL is so special in
bridging and molecular construction that it is good in keeping and
reproducing the shape. The key property of .alpha.GEL is being
independent of temperature in vibration isolation, shock-absorbing,
and soundproofing. .alpha.GEL shows the properties in wide range of
temperature, while other materials show their properties only at
ordinary temperatures. Also, .alpha.GEL stably shows the properties
such as heat-resistance, cold-resistance, weather-resistance, and
safety.
In addition, instead of silicone, rubber isolators such as urethane
high dumping rubber, polynorbornene rubber, polyisobutyl rubber,
natural: rubber, and EPDM rubber (Ethylen-Propylen-Dien-Monomer
rubber) can be used for damping member 20.
As described above, the lens driving device in the present
invention is held by the base via the viscoelastic damping member,
and the damping member suppresses the oscillations of the lens in
any direction through its vibration suppressing action. By using
this lens driving device in order to move an lens of an optical
pickup, the lens driving device prevents undesired oscillations of
optical members, so that the optical pickup can read and write the
information of an optical recording medium properly.
Here, because the lens is held directly by the base via the damping
member, the size of the lens driving device become smaller than
conventional lens driving devices that is held like a cantilever
via a plurality of linear elastic supporting members.
Although the present invention has been fully described by way of
examples with reference to the accompanying drawings, it is to be
noted that various changes and modifications will be apparent to
those skilled in the art.
Therefore, unless otherwise such changes and modifications depart
from the scope of the present invention, they should be construed
as being included therein.
* * * * *